c++ 单例模式最佳写法

pthread_once

class Singleton {
public:
static Singleton *GetInstance() {
pthread_once(&ponce_, &Singleton::init);
return value_;
}
private:
Singleton() {}
Singleton(const Singleton &);
Singleton& operator= (const Singleton &);
static void init() {
value_ = new T();
}
static pthread_once_t ponce_;
static Singleton *value_;
};
pthread_once_t SIngleton::ponce_ = PTHREAD_ONCE_INIT;
Singleton* Singleton::value_ = NULL;
---------------------

饿汉模式
必须在main开始前就初始化好，于是，需要一个静态变量。可以是对象，也可以是对象的指针。如果是指针，在main开始前new一下就行。由于这个静态变量只会被单例类使用，所以最好不是静态全局变量，而是类的静态成员变量。

// 对象版
// singleton.h
class Singleton {
private:
Singleton() {}
Singleton(const Singleton &);
Singleton& operator= (const Singleton &);
static Singleton s;
public:
static Singleton *GetInstance() {
return &s;
}
};
// singleton.cc
Singleton Singleton::s;

还有：

//指针版。没有析构逻辑，会造成泄露。
// singleton.h
class Singleton {
private:
Singleton() {}
Singleton(const Singleton &);
Singleton& operator= (const Singleton &);
static Singleton *p;
public:
static Singleton *GetInstance() {
return p;
}
};
// singleton.cc
Singleton *Singleton::p = new Singleton;

 

 

class Singleton
{
private:
static Singleton* m_instance;
Singleton(){}
public:
static Singleton* getInstance();
};

Singleton* Singleton::getInstance()
{
if(NULL == m_instance)
{
Lock();//借用其它类来实现，如boost
if(NULL == m_instance)
{
m_instance = new Singleton;
}
UnLock();
}
return m_instance;
}

 

 

 

 

 

 

 

====================

MasterConf* MasterConf::instance_ = NULL;

pthread_mutex_t MasterConf::mutex_ = PTHREAD_MUTEX_INITIALIZER;

MasterConf* MasterConf::GetInstance() {
if (NULL == instance_) {
pthread_mutex_lock(&mutex_);
if (NULL == instance_) {
instance_ = new MasterConf();
}
pthread_mutex_unlock(&mutex_);
}

return instance_;
}